Food allergy testing

[Patch test in the diagnosis of food allergy]

Food allergens are capable of producing adverse reactions through multiple mechanisms of an allergic or non-allergic nature, and through different routes of exposure; generally by ingestion or contact, as in protein contact dermatitis or contact urticaria, including inhalation. Food allergy reactions, in turn, can be mediated by immediate hypersensitivity mechanisms, delayed hypersensitivity or mixed immediate-delayed mechanisms. The reference diagnostic method in food allergy is the double-blind placebo-controlled food challenge test (DBPCFC), but skin and serological tests are important in the clinical context. The diagnosis of immediate food allergy depends on well-standardized allergological tests, such as the skin prick test (SPT) or specific IgE dosing, which are ideally tested by food challenge testing. However, the diagnosis of delayed mechanism food allergy and mixed allergies, which combine both immune mechanisms, is more complex. Delayed hypersensitivity reactions are evaluated with the epicutaneous patch test, or patch testing, for the diagnosis of contact dermatitis. The atopy patch test is initially used for the investigation of inflammatory reactions, which may be linked to food allergens in patients with atopic dermatitis. It was later applied in other diseases, whose pathogenesis is mainly mediated by a mechanism of delayed hypersensitivity to protein allergens: eosinophilic esophagitis, enterocolitis induced by food proteins, protein contact dermatitis, contact urticaria, among other disorders.

Hair and saliva test fails to identify allergies in dogs

OBJECTIVES

Several companies offer saliva and/or hair tests for food and environmental allergies in companion animals, but provide no validation of test accuracy. We examined one such hair and saliva allergy test to determine whether it could reliably differentiate between a normal dog and an allergic dog, and to examine test repeatability.

MATERIALS AND METHODS

Ten fur and saliva samples were submitted from a known allergic dog and a normal, non-allergic dog. Five fake fur samples and water were also submitted to determine whether the test could differentiate between a real dog and toy animal. The company performed testing for 128 food and environmental allergens. Statistical analyses were performed to determine whether the response distribution differed significantly between dogs, using the Pearson chi-square coefficient, as well as to determine test-retest reliability by calculating Cohen's kappa for each allergen.

RESULTS

The distribution of test results from samples obtained from allergic, non-allergic or fake dogs was not different from that expected due to random chance. Test-retest reproducibility was poor to slight.

CLINICAL SIGNIFICANCE

Hair and saliva testing should not be used to diagnose allergies and is not a substitute for veterinary-directed allergy evaluation and diagnostics.